In an electrical communication system, it is sometimes advantageous to transmit data in the form of differential signals over a pair of conductive paths (i.e., a conductive path pair) rather than a single conductive path, where the transmitted signal comprises the voltage difference between the conductive paths without regard to the absolute voltages present. Each conductive path in a conductive path pair is capable of picking up electrical noise from outside sources, e.g., neighboring data lines, or other sources. Differential signals may be advantageous to use due to the fact the signals are less susceptible to these outside sources.
A concern with differential signals is electrical noise that is caused by neighboring differential conductive path pairs, where the individual conductors on each conductive path pair couple (inductively or capacitively) in an unequal manner that results in added noise to the neighboring conductive path pair. This is referred to as crosstalk. Crosstalk can occur on a near-end (NEXT) and a far-end (FEXT) of a transmission line between differential conductive path pairs within a channel (referred to as internal NEXT and internal FEXT) or can couple to differential conductive path pairs in a neighboring channel (referred to as alien NEXT and alien FEXT). Generally speaking, so long as the same noise signal is added to each conductive path in the conductive path pair, then the voltage difference between the conductive paths will remain about the same and crosstalk is minimized.
In the communications industry, as data transmission rates have steadily increased, crosstalk due to capacitive and inductive couplings among the closely spaced parallel conductors within the plug and/or jack has become increasingly problematic. Modular connectors with improved crosstalk performance have been designed to meet the increasingly demanding standards. For example, recent connectors have introduced predetermined amounts of crosstalk compensation to cancel offending NEXT, which, in turn, gives the system an increased bandwidth. This crosstalk compensation is typically implemented in two or more stages for certain conductive path pair combinations, to account for phase differences between couplings in the plug and the jack. These two or more stages have been generally necessary because the source of the crosstalk is at the plug, which is at an increasing electrical distance (phase difference) from the source of the compensation (at the jack) with increasing frequency. With two stages, the phase and polarity differences between each stage are chosen such that they provide cancellation of the crosstalk and typically increase the NEXT bandwidth of the system. However, the two stage compensation scheme requires twice as many capacitors as would be minimally necessary in order to cancel the offending crosstalk from the plug. The addition of these extra capacitors may degrade return loss and create issues in production where minor manufacturing variations in the capacitors lead to jack failures. Thus, there is a continuing need to design new and improved compensation methods and devices.